1. Technical Field
The present invention relates to human small cell lung cancer (SCLC) autocrine growth factors and monoclonal antibody blocking the same. More particularly, the present invention relates to anti-bombesin monoclonal antibody blocking bombesin-receptor interaction at appropriate binding sites and inhibiting tumor growth dependent on bombesin autocrine function.
2. Prior Art
Autocrine hypothesis for tumor growth proposes that a cancer cell produces a growth factor(s) which in turn stimulates the growth of the cancer cell resulting in a malignant phenotype (Sporn, et al. New Eng. J. Med. 303, (1980). If this hypothesis is demonstrated to be true, then it would be apparent that by interfering with this autocrine pathway, one could potentially block tumor cell growth dependent on said autocrine growth factor.
By definition autocrine growth factors comprise hormone-like substances produced and secreted by normal or malignant cells which in turn "feed back" on these cells via specific membrane receptors to induce proliferation of the cells. Although many growth factors (epidermal growth factor [EGF], transforming growth factors [TGF], platelet-derived growth factor [PDGF], T-cell growth factor [ITCGF], nerve growth factor [NGF] and the like have been shown to exert their influence on the propagation of normal and malignant cells in vitro, none so far has been conclusively proven to fulfill all the autocrine properties including control of tumor proliferation in vitro.
Lung cancers have been the prime example of tumors which produce peptide hormones. Within this group, human small cell lung cancer (SCLC) has been shown to produce regulatory peptides such as calcitonin, adrenocorticotrophic hormone (ACTH), arginine vasopressin (AVP), neurotensin and bombesin. Bombesin is the most frequently produced peptide hormone associated with SCLC; therefore, it has been considered a putative autocrine growth factor involved with SCLC.
Bombesin is a tetradecapeptide originally isolated and characterized by Anastasi, et al. Experientia 27, 166-167 (1971) from frog skin. Immunoreactive bombesin-like peptides (BLP) have also been identified in fish, birds, and mammals indicating evolutionary conservation. Biochemical and immunohistochemical analyses have localized BLP to certain brain nuclei, to amine precursor uptake and decarboxylation (APUD) cells of the fetal lung, and to gastrointestinal tract of rat and man as well as the proventriculus of turkeys. The mammalian equivalent of bombesin is thought to be gastrin-releasing peptide (GRP), a 27 amino acid long peptide initially isolated from porcine gut as described by McDonald, et al, Gut, 19: 767. (1978). Bombesin and GRP have nearly identical amino acid sequences at their carboxy-terminal (C-terminal) decapeptide.
The carboxy-terminal region of the bombesin molecule is believed to be responsible for receptor recognition and biological activity. Recent reports have demonstrated that both bombesin and GRP can induce similar biological responses (Brown, et al. Life Sci. 27, 125-128 (1980; Rokaeus, et al. Acta Physiol. Scand. 114, 605-610 (1982); Girard, et. al. Neuropeptides 3, 443-452 (1983); McDonald, et. al. Regul. Peptides 5, 125-137 (1983). Immunoreactive GRP has been identified in the gastrointestinal tract of mice, rats, guinea-pigs and cats. Amino acid sequences of three canine intestinal peptides have revealed close homology with porcine GRP and contain identical C-terminal decapeptide residues as bombesin and GRP (Reeve, et al J. Bio. Chem. 258, 5582-5588 (1983). In humans, GRP has been identified in neuro-endocrine cells of the stomach, fetal and adult lung and in small cell and carcinoid lung tumors. (Tsutsumi, et el. Lab. Invest. 48, 623-631 (1983); Yamaguchi, et el. Cancer Res. 43, 3932-3939 (1983); Tobe, et al. Acta Histochem. Cytochem. 15, 102-107 (1982); Tamai, et al. Cancer 52, 273-281 (1983); Yang, et el. Cancer 52, 819-823 (1983).
In recent reviews, bombesin (BN) and bombesin-like peptides (BLP) have been reported to initiate a wide variety of physiological responses including stimulation of SCLC. BLP produced by SCLC include some peptides similar, if not identical, to porcine GRP. These peptides can be secreted into media in response to physiologic stimuli. In addition, some SCLC have single class of high affinity receptors for BLP (Moody, et al. Peptides 4, 683-686 (1983). Moreover, exogenously added BLP can stimulate the clonal growth of SCLC in serum-free medium (Carney, et al. Clin. Res. 31, 404A (1983). Taken together, these findings suggest, but do not prove, that BLP could function as an autocrine growth factor for SCLC. The applicants conceived that one way to test such a hypothesis would be to interrupt the function of endogenously produced BLP in SCLC. The applicants reasoned that this could be accomplished by producing antibodies specific to BN or BLP.